The present invention relates generally to tools used to complete subterranean wells and, in a preferred embodiment thereof, more particularly provides apparatus for use in gravel pack operations and methods of using same.
Gravel pack operations are typically performed in subterranean wells to prevent fine particles of sand or other debris from being produced along with valuable fluids extracted from a geological formation. If produced (i.e., brought to the earth's surface), the fine sand tends to erode production equipment, clog filters, and present disposal problems. It is, therefore, economically and environmentally advantageous to ensure that the fine sand is not produced.
In the subterranean well, a tubular protective casing usually separates the formation containing the fine sand particles from the wellbore. The casing is typically perforated opposite the formation to provide flowpaths for the valuable fluids from the formation to the wellbore. If production tubing is simply lowered into the wellbore and the fluids are allowed to flow directly from the formation, into the wellbore, and through the production tubing to the earth's surface, the fine sand will be swept along with the fluids and will be carried to the surface by the fluids.
Conventional gravel pack operations prevent the fine sand from being swept into the production tubing by installing a sand screen on the end of the production tubing. The wellbore in an annular area between the screen and the casing is then filled with a relatively large grain sand (i.e., "gravel"). The gravel prevents the fine sand from packing off around the production tubing and screen, and the screen prevents the large grain sand from entering the production tubing.
A problem, which is present in every conventional gravel pack operation, is how to place the gravel in the annular area between the screen and the casing opposite the formation. If the screen is merely attached to the bottom of the production tubing when it is installed in the wellbore, the gravel cannot be pumped down the production tubing because the screen will prevent it from exiting the tubing. The gravel cannot be dropped into the wellbore annular area from the earth's surface because a packer is usually installed between the production tubing and the casing above the formation, and this method would be very inaccurate in packerless completions as well.
One solution has been to run the production tubing into the wellbore without the screen being attached to the tubing. A landing nipple is installed at or near the bottom of the tubing before running the tubing into the well. When the landing nipple has been properly positioned above the formation, a screen is lowered into the tubing from the earth's surface on a slickline or wireline. The screen is landed in the nipple in the tubing so that it extends outwardly and downwardly from the tubing and is positioned opposite the formation. Gravel is then pumped down the tubing from the earth's surface, through a small space between the nipple and the screen, and outwardly into the annular area between the screen and the casing opposite the formation. This method is known as "through tubing gravel packing", since the gravel is pumped through the tubing.
This method has several disadvantages, however. One disadvantage is that the screen must be installed into the tubing as a separate operation. This requires coordination with a slickline or wireline service, time spent rigging up and rigging down special equipment such as lubricators needed for these operations, and the inability to conveniently perform such operations in wells which are horizontal or nearly horizontal. In some instances, the screen is run in with the tubing, already landed in the nipple in the tubing. In those instances, a slickline operation is still needed to retrieve the screen from the tubing.
Another disadvantage of the above method is that the screen must be able to pass through the tubing. This means that the size of the screen (at least its outer diameter) can be no larger than the tubing's inner drift diameter. In order to have a sufficiently large screen surface area, very long screens must sometimes be utilized with this method. Additionally, since there is usually only a very small radial gap between the screen (or the slickline tool used to place the screen in the nipple) and the landing nipple, only a very small flow area is available for pumping the gravel out of the tubing and into the annular area of the well.
Yet another disadvantage of the above method is that the tubing may not be conveniently removed from the wellbore for replacing the packer, completing other formations in the well, maintenance, etc. The method requires the screen to be removed along with the tubing, or the screen must be removed by wireline or slickline prior to removing the tubing. In either case, the gravel pack will be destroyed as the gravel falls into the void created when the screen is removed.
From the foregoing, it can be seen that it would be quite desirable to provide apparatus for gravel pack operations which does not require the screen to be positioned as a separate operation and does not require the screen to pass through the tubing, but which provides a large flow area for pumping the gravel into the annular area of the well and provides for convenient detachment of the tubing from the screen for removal of the tubing from the wellbore. It is accordingly an object of the present invention to provide such apparatus and associated methods of using same.